1. Field of the Invention
The present invention relates to a cross-fed FET power-chip for use for example as a basic power amplifier in a distributed transmitter of an antenna array. More specifically, a power-chip is implemented in gallium arsenide reducing the number of components by employing broadband couplers and four port directional couplers between stages eliminating as many as fifty components per chip and employing combiners to combine the outputs of the stages, with a large percentage of the output of each stage going to the combiner and a smaller percentage going to the input of the next stage.
2. Description of the Prior Art
A prior art FET power amplifier such as shown in FIG. 1 achieves high RF power by combining ten cells, S.sub.1 -S.sub.10, gate size 2.4 mm each. Each cell has internal input and output matching. The final part of the divider and combiner circuits is external to the chip in order to keep the physical size of the chip reasonable.
The disadvantages of the prior art device are inherently high cost, moderate band width and a low gain for the following reasons. Each input impedance matching network for the FET F.sub.1 requires five elements, L.sub.0, L.sub.2, L.sub.4, C.sub.1 and C.sub.3 or a total of fifty elements for ten cells. This configuration drives up the chip's size and cost for large volume production. The amplifier bandwidth is limited by the high transforming ratio, 1.5 ohms to 50 ohms. A low impedance ten way divider is needed at the input for drive distribution. Also the need for high input power level dictates a medium power driver for module application which makes parallel combining of chips exceedingly difficult.
Another prior art device is disclosed in U.S. Pat. No. 4,788,511, Schindler, Distributed Power Amplifier. In this device, each amplifier needs its own network which is then combined.
U.S. Pat. No. 4,514,699, Kariatsumari, et al., discloses a microwave power amplifier combiner composed of .rho./2 hybrid couplers which employ reflector type amplifiers different from the amplifiers of the subject invention.
U.S. Pat. No. 3,534,283 Seidel, employs a series of emitter follower amplifiers in which each stage drives the next, whereas the present invention derives power from each stage.
U.S. Pat. No. 3,919,685, Haill, Seismic Data Acquisition System, discloses an amplifier employing standard parallel combining by means of switching.